This invention relates to the binaural reproduction of sound. More particularly, this invention relates to apparatus for the precise reproduction or transmission of sound so that the sound waves which reach the listener's eardrum are substantially identical to those reaching the eardrums of the persons actually present within the originating sound field.
Apparatus and techniques for the faithful reproduction of sound have been the subject of a great deal of development effort throughout the past few decades. The benefits of high-quality sound reproduction have become well known and include increased listening pleasure of musical compositions and increased intelligibility of oral communications under difficult circumstances such as speakers who are located in extremely noisy environments.
In the area of recording and reproducing musical entertainment alone, many significant changes have occurred in the past few years. The monophonic high-fidelity systems of the 1950's have been largely supplanted by the stereophonic techniques of the 1960's which, along with the increasingly popular four-channel or quadraphonic systems, form the present-day quality sound system. Although each system has demonstrated an advance over the preceding systems, complete realism has not been achieved by currently available apparatus, and those within the art continually strive to achieve sound reproduction which, in effect, places the listener in the audience.
One recent stereophonic system of interest attempts to produce electrical signals which faithfully represent what a person actually located in the sound field of interest would hear by utilizing microphones positioned to duplicate the human ears. In some instances, the microphones have been actually placed on or encased in a mannequin or model of a head in an attempt to capture the sound as it is actually heard by a physically present listener, influenced by head and ear size, bone construction, and other factors. If the signal recorded by such a system is reproduced in a quality stereo apparatus and presented to the listener by means of a stereophonic headset, a marked improvement in directionality is observed, that is, the listener's ability to determine the relative location of each particular sound source contributing to the overall recorded sound field is enhanced. This improvement in directionality, in turn, imparts the sensation of greater realism. For example, where the reproduced sound is musical entertainment, the listener's sense of impression as to the localization of each musical instrument and each voice is greatly improved, and where the reproduced sound is speech in which there is either a high background noise level or several speakers engaging in rapid conversational exchange, the listener's ability to ascertain what is said by a speaker is significantly enhanced. Although this prior art system has demonstrated improved directionality and realism, it has not achieved that degree of improvement over more conventional recording and reproduction systems required to create widespread interest and application.
Accordingly, it is an object of this invention to provide a binaural sound reproduction system which exhibits greater realism and directionality characteristics than those exhibited by the prior art.
It is a further and more specific object of this invention to utilize recent advances in the understanding of the human auditory tract to realize a system in which the recorded sound is representative of the sound pressure developed at a listener's eardrum, rather than the sound pressure which would impinge on the outer ear, and to realize a novel in-ear transducer or receiver unit which exhibits a flat frequency response as measured at the listener's eardrums.